FUNCTION YLINTP (XINT,X,Y,N,NTOT)
C     =================================
C
C     linear interpolation routine. Determines YINT = Y(XINT) from 
C     grid Y(X) with N points and dimension NTOT. 
C
      INCLUDE 'PARAMS.FOR'
      DIMENSION X(NTOT),Y(NTOT)
C
C     bisection (see Numerical Recipes par 3.4 page 90)
      JL = 0
      JU = N+1
10    IF (JU-JL.GT.1) THEN
         JM = (JU+JL)/2
         IF ((X(N).GT.X(1)).EQV.(XINT.GT.X(JM))) THEN
            JL = JM
         ELSE
            JU = JM
         END IF
         GO TO 10
      END IF
      J = JL
      IF (J.EQ.N) J = J-1
      IF (J.EQ.0) J = J+1
      RC         = (Y(J+1)-Y(J))/(X(J+1)-X(J))
      YLINTP = RC*(XINT-X(J))+Y(J)
C
      RETURN
      END